Adding too many indexes to a table and duplicating indexes
on the same field can hurt performance and increase your database size.

Not every field name that begins or ends with the
default values should have a secondary index.

Some fields have only a few unique values, so secondary
indexes on those fields are not very helpful

Some fields that aren't named that way may need
secondary indexes, so using the default setting is not a wise solution
since thought should be put into this.

Some secondary indexes may involve more than one field,
so single field indexes may not be helpful.

Significant Problems on Table Import

When you import a table with these settings, the indexes are
added to your new table automatically. That may be fine for a brand new
table, but if you are importing a table to replace an existing table (from a
backup) or creating a new database by importing all the tables from an
existing database, a whole set of new secondary indexes may be added
unnecessarily -- essentially undoing the work you may have done to determine
which fields shouldn't have indexes.

If you understand when to add secondary indexes on your
tables, you should set the AutoIndex on Import/Create option to nothing.
This lets you control where and when indexes are added, and eliminates it
from happening by chance:

If you have our Total Access Analyzer program, this setting is one of
the ~300 issues detected when your database is documented. Learn more about how Total Access Analyzer can help you
create better
Microsoft Access applications.